The U.S. military utilizes M2 and M85 machine guns, firing fifty caliber (hereinafter ‘.50″ caliber’) projectiles, to penetrate and destroy hard targets at long ranges, up to and about 800 meters. The .50″ caliber projectiles including M2 armor piercing rounds are designed to penetrate light-armored vehicles or breach hard unarmored targets such as concrete walls or shelters.
Other .50″ caliber projectiles, such as the M1 or M23 incendiary rounds contain an incendiary composition, such that upon impact the composition bursts into flame, to ignite any flammable material in proximity thereof. These incendiary rounds may be used against aircraft.
Certain .50″ machine gun projectiles of particular interest include the M8 armor piercing incendiary (API) round and the MK257 armor piercing incendiary dim tracer (API-DT) round, which rounds combines the functionality of the M2 armor piercing round and the M1/M23 incendiary rounds; so as to be useful against hard targets containing a flammable component, such as lightly armored targets containing volatile fuels, e.g. aviation fuel, gas, diesel fuel, etc. Upon impact with such a hard target, the M8/MK257 round will penetrate the target, the kinetic energy of the impact is converted by friction to heat which causes an incendiary material within the projectile to ignite, such as U.S. incendiary composition IM-11 (50% barium nitrate and 50% powdered aluminum/magnesium alloy) or IM-28. Importantly, in addition to providing a means for igniting flammable materials, including fuel vapors, in or about the target; the ignition of the incendiary provides an incandescent flash, which is very useful for marking the impact point—as a pyrotechnic signal to other military units.
The M8 API, MK257 (API-DT) and other similar in-service U.S. military incendiary projectiles, such as the 20 mm PGU-28/B semi armor piercing high explosive incendiary (SAPHEI) and the 20 mm M940 multi-purpose tracer with self destruct (MPT-SD) round, contain potassium perchlorate (KClO4) and/or barium nitrate, as an oxidizer, within their oxidizer/fuel incendiary composition. These compounds however, have been associated with toxic effects in humans. For instance, potassium perchlorate has been associated with increasing thyroid dysfunction and teratogenicity while barium nitrate has been reported as being cardiotoxic. Further, while recent work has shown that sodium nitrate (NaNO3) can be a substitute for such environmentally toxic oxidizers, the hygroscopic nature of NaNO3 promotes agglomeration upon exposure to water vapor in the air which poses risks during manufacturing and affects performance of the pyrotechnic projectiles.
Therefore, a need exists in the art for a less toxic alternative oxidizer to potassium perchlorate and barium nitrate in armor piercing incendiary projectile compositions—an alternative that does not suffer from being hygroscopic. In addition, the alternative oxidizer must provide equally reliable ignition, burn time and pyrotechnic visual intensity to the current incendiaries based on barium nitrate and potassium perchlorate oxidizers.